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RFC 950

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    Network Working Group
    Request for Comments: 950

    J. Mogul (Stanford)
    J. Postel (ISI)
    August 1985

### Internet Standard Subnetting Procedure

### Status Of This Memo

This RFC specifies a protocol for the ARPA-Internet community. If subnetting is implemented it is strongly recommended that these procedures be followed. Distribution of this memo is unlimited.

### Overview

This memo discusses the utility of "subnets" of Internet networks, which are logically visible sub-sections of a single Internet network. For administrative or technical reasons, many organizations have chosen to divide one Internet network into several subnets, instead of acquiring a set of Internet network numbers. This memo specifies procedures for the use of subnets. These procedures are for hosts (e.g., workstations). The procedures used in and between subnet gateways are not fully described. Important motivation and background information for a subnetting standard is provided in RFC-940 [7].

### Acknowledgment

This memo is based on RFC-917 [1]. Many people contributed to the development of the concepts described here. J. Noel Chiappa, Chris Kent, and Tim Mann, in particular, provided important suggestions. Additional contributions in shaping this memo were made by Zaw-Sing Su, Mike Karels, and the Gateway Algorithms and Data Structures Task Force (GADS).

### Table of Contents

1. Motivation
2. Standards for Subnet Addressing

2.1. Interpretation of Internet Addresses
2.2. Changes to Host Software to Support Subnets
2.3. Finding the Address Mask

Appendix I. Address Mask ICMP
Appendix II. Examples

1. A Class A Network Case
2. A Class B Network Case
3. A Class C Network Case (illustrating non-contiguous subnet bits)

Appendix III. Glossary
Appendix IV. Assigned Numbers

References

Original text document

Connected: An Internet Encyclopedia
RFC 950